Antiwear Composition and Method of Lubricating Driveline Device

ABSTRACT

The present invention relates to an antiwear agent and lubricating compositions thereof. The invention further provides for a method of lubricating a driveline device application by employing a lubricating composition containing the antiwear agent.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. Ser. No.13/390,790 filed on May 9, 2012, which claims priority to provisionalapplication Ser. No. 61/234,722 filed on Aug. 18, 2009.

FIELD OF INVENTION

The present invention relates to an antiwear agent and lubricatingcompositions thereof. The invention further provides for a method oflubricating a driveline device by employing a lubricating compositiondescribed herein.

BACKGROUND OF THE INVENTION

One of the important parameters influencing durability or wearresistance of devices employing a lubricating composition is theeffectiveness of phosphorus antiwear or extreme pressure additives atproviding devices with appropriate protection under various conditionsof load and speed. However, many of the phosphorus antiwear or extremepressure additives contain sulphur. Due to increasing environmentalconcerns, the presence of sulphur in antiwear or extreme pressureadditives is becoming less desirable. In addition, many of thesulphur-containing antiwear or extreme pressure additives evolvevolatile sulphur species, resulting in lubricating compositionscontaining antiwear or extreme pressure additives having an odour, whichmay also be detrimental to the environment or evolve emissions that maybe higher than increasingly tighter health and safety legislationspecifies.

A lubricating composition having the correct balance of phosphorusantiwear or extreme pressure additives provides driveline powertransmitting devices with prolonged life and efficiency with controlleddeposit formation and oxidation stability. However, many of the antiwearor extreme pressure additives employed have at least one of (i) limitedextreme pressure and antiwear performance over a wide range of operatingconditions, (ii) limited oxidative stability, (iii) form deposits, or(iv) cause corrosion (for example copper corrosion). In addition, manyphosphorus antiwear or extreme pressure additives typically containsulphur, which results in an odorous lubricating composition containingthe phosphorus antiwear or extreme pressure additives. A number ofreferences disclosing antiwear chemistry are discussed below.

U.S. Pat. No. 5,338,470 discloses alkylated citric acid derivativesobtained as a reaction product of citric acid and an alkyl alcohol oramine. The alkylated citric acid derivative is effective as an antiwearagent and friction modifier.

U.S. Pat. No. 4,237,022 discloses tartrimides useful as additives inlubricants and fuels for effective reduction in squeal and friction aswell as improvement in fuel economy.

U.S. Pat. No. 4,952,328 discloses lubricating oil compositions forinternal combustion engines, comprising (A) oil of lubricatingviscosity, (B) a carboxylic derivative produced by reacting a succinicacylating agent with certain amines, and (C) a basic alkali metal saltof sulphonic or carboxylic acid.

U.S. Pat. No. 4,326,972 discloses lubricant compositions for improvingfuel economy of internal combustion engines. The composition includes aspecific sulphurised composition (based on an ester of a carboxylicacid) and a basic alkali metal sulphonate.

International publication WO 2008/070307 discloses malonate esterssuitable as antiwear agents.

International Patent application WO US09/036623 (Filed Mar. 10, 2009 byNajman) discloses a driveline device lubricated with a compositioncontaining a derivative of a hydroxycarboxylic acid and a phosphoruscompound that may be either (i) a hydroxy-substituted di-ester of(thio)phosphoric acid, or (ii) a phosphorylated hydroxy-substituted di-or tri-ester of (thio)phosphoric acid.

International publication WO 2005/087904 discloses lubricants containinghydroxy carboxylic acid and hydroxy polycarboxylic acid esters incombination with phosphorus-containing additives. Thephosphorus-containing additives include zincdihydrocarbyldithiophosphates and/or neutral phosphorus compounds, suchas trilauryl phosphate or triphenylphosphorothionate. The lubricants areuseful in engine lubricants.

International publication WO 2006/044411 discloses a low-sulphur,low-phosphorus, low-ash lubricant composition containing a tartrateester, or amide having 1 to 150 carbon atoms per ester or amide group.The lubricant composition is suitable for lubricating an internalcombustion engine.

SUMMARY OF THE INVENTION

The inventors of this invention have discovered that a lubricatingcomposition and method as disclosed herein is capable of providingacceptable levels of at least one of (i) sulphur (typically reducing orpreventing emissions from waste oil), (ii) fuel economy/efficiency(typically improving fuel economy/efficiency), (iii) oxidation control(typically reducing or preventing oxidation), (iv) friction performance,(v) wear and/or extreme pressure performance (typically reducing orpreventing wear), and (vi) deposit control. Wear may include reducedrippling, ridging and scoring. The wear may be observed on a ring and/orpinion of a driveline device.

In one embodiment the invention provides a lubricating compositioncomprising an oil of lubricating viscosity and an antiwear package,wherein the antiwear package comprises (a) a derivative of ahydroxycarboxylic acid, and (b) a phosphorus compound selected from thegroup consisting of an amine salt of a phosphate hydrocarbon ester, aphosphite having at least one hydrocarbyl group with 4 or more carbonatoms, and mixtures thereof. In one embodiment the phosphorus compoundis a mixture of an amine salt of a phosphate hydrocarbon ester, and aphosphite having at least one hydrocarbyl group with 4 or more carbonatoms.

In one embodiment the invention provides a method for lubricating adriveline device comprising supplying to the driveline device alubricating composition comprising an oil of lubricating viscosity andan antiwear package wherein the antiwear package comprises (a) aderivative of a hydroxycarboxylic acid, and (b) a phosphorus compoundselected from the group consisting of an amine salt of a phosphatehydrocarbon ester, a phosphite having at least one hydrocarbyl groupwith 4 or more carbon atoms, having at least one hydrocarbyl group with4 or more carbon atoms, and mixtures thereof.

In one embodiment the derivatives of hydroxycarboxylic acid includeimides, di-esters, di-amides, ester-amides derivatives of tartaric acid.

In one embodiment the phosphorus compound may be an amine salt of aphosphate hydrocarbon ester, or mixtures thereof.

In one embodiment the lubricating composition disclosed herein contains

(a) the derivative of a hydroxycarboxylic acid present at 0.01 wt % to 3wt %, or 0.01 wt % to 1 wt %, or 0.05 wt % to 0.5 wt %, or 0.1 wt % to0.2 wt % (typically 0.05 wt % to 0.5 wt %) of the lubricatingcomposition; and

(b) the phosphorus compound present at 0.01 wt % to 5 wt %, or 0.05 wt %to 2 wt %, or 0.1 wt % to 1 wt %, or 0.2 wt % to 0.4 wt % (typically 0.1wt % to 1 wt %) of the lubricating composition.

In different embodiments the lubricating compositions disclosed hereincontain 0 ppm to 500 ppm, or 5 ppm to 300 ppm, or 20 ppm to 250 ppm ofmolybdenum.

In different embodiments the lubricating compositions disclosed hereinmay have a sulphur-content of greater than 0.3 wt %, or 0.4 wt % to 5 wt%, or 0.5 wt % to 3 wt %, 0.8 wt % to 2.5 wt %, or 1 wt % to 2 wt % ofthe lubricating composition.

In one embodiment the invention provides for the use of a lubricatingcomposition as disclosed herein for providing acceptable levels of atleast one of (i) phosphorus emissions, (ii) sulphur emissions, (iii)fuel economy/efficiency, (iv) oxidation control, (v) frictionperformance, (vi) wear and/or extreme pressure performance (typicallywear reducing or preventing), and (vii) deposit control.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a lubricating composition; and a methodfor lubricating a driveline device as disclosed above.

Compound Derived from Hydroxy-Carboxylic Acid

The invention provides a lubricating composition containing a compoundderived from a hydroxy-carboxylic acid. The compound derived from ahydroxy-carboxylic acid may be represented by the formula:

whereinn and m may be independently integers of 1 to 5;X may be an aliphatic or alicyclic group, or an aliphatic or alicyclicgroup containing an oxygen atom in the carbon chain, or a substitutedgroup of the foregoing types, said group containing up to 6 carbon atomsand having n+m available points of attachment;each Y may be independently —O—, or >NR¹ or two Ys together mayrepresent the nitrogen of an imide structure R—N<formed between twocarbonyl groups; andeach R and R¹ may be independently hydrogen or a hydrocarbyl group,provided that at least one R or R¹ group is a hydrocarbyl group; each R²may be independently hydrogen, a hydrocarbyl group or an acyl group,further provided that at least one —OR² group is located on a carbonatom within X that is α or β to at least one of the —C(O)—Y—R groups.

The compound derived from the hydroxy-carboxylic acid may be derivedfrom glycolic acid (n and m both equal 1), malic acid (n=2, m=1),tartaric acid (n and m both equal 2), citric acid (n=3, m=1), ormixtures thereof. In one embodiment the compound derived from thehydroxy-carboxylic acid may be derived from tartaric acid or citricacid. In one embodiment the compound derived from the hydroxy-carboxylicacid may be derived from tartaric acid.

The compound derived from the hydroxy-carboxylic acid may be an amide,ester or imide derivative of a hydroxy-carboxylic acid, or mixturesthereof. In one embodiment the compound derived from thehydroxy-carboxylic acid may be an amide, ester or imide derivative of ahydroxy-carboxylic acid. For example the compound derived from thehydroxy-carboxylic acid may an ester or imide of tartaric acid, or thecompound derived from the hydroxy-carboxylic acid may an ester or imideof citric acid.

In one embodiment the compound derived from the hydroxy-carboxylic acidmay be at least one of a hydroxy-carboxylic acid di-ester, ahydroxy-carboxylic acid di-amide, a hydroxy-carboxylic acid di-imide, ahydroxy-carboxylic acid mono-imide, a hydroxy-carboxylic acidester-amide, a hydroxy-carboxylic acid ester-imide, and ahydroxy-carboxylic acid imide-amide. In one embodiment the amide, esteror imide derivative of a hydroxy-carboxylic acid may derived from atleast one of the group consisting of a hydroxy-carboxylic acid di-ester,a hydroxy-carboxylic acid di-amide, a hydroxy-carboxylic acidmono-imide, and a hydroxy-carboxylic acid ester-amide.

Each R, R¹ and R² group of the compound derived from thehydroxy-carboxylic acid may be a linear or branched alkyl group eachhaving 1 to 150, or 8 to 30, or 8 to 20 carbon atoms. The esterderivatives of the hydroxy-carboxylic acid may be formed by the reactionof an alcohol with hydroxy-carboxylic acid. The alcohol includes bothmonohydric alcohols and polyhydric alcohols. The carbon atoms of thealcohol may be linear chains, branched chains, or mixtures thereof.

Examples of a suitable branched alcohol include 2-ethylhexanol,iso-tridecanol, iso-octyl alcohol, Guerbet alcohols, or mixturesthereof.

Examples of a monohydric alcohol include methanol, ethanol, propanol,butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol,undecanol, dodecanol, tridecanol, tetradecanol, pentadecanol,hexadecanol, heptadecanol, octadecanol, nonadecanol, eicosanol, ormixtures thereof. In one embodiment the monohydric alcohol contains 8 to20 carbon atoms.

In one embodiment the imide derivatives of a hydroxy-carboxylic acid maybe tartrimides, typically containing 8 to 20 carbon atoms. Amines usedto prepare imides may include alkyl amines (such as n-hexylamine(caproylamine), n-octylamine (caprylylamine), n-decylamine(caprylamine), n-dodecylamine (laurylamine), n-tetradecylamine(myristylamine), n-pentadecylamine, n-hexadecylamine (palmitylamine),margarylamine, n-octadecylamine (stearylamine)), unsaturated amines(such as dodecenylamine, myristoleylamine, palmitoleylamine, oleylamine,and linoleylamine), or etheramines (such as those identified as SURFAM™P 14AB (branched C14), SURFAM™ P 16A (linear C16), and SURFAM™ P 17AB(branched C17)). A detailed description of methods for preparingsuitable tartrimides (by reacting tartaric acid with a primary amine) isdisclosed in U.S. Pat. No. 4,237,022.

U.S. Patent Applications 60/939,949 (filed May 24, 2007) and U.S.60/939,952 (filed May 24, 2007) disclose in more detail usefulhydroxycarboxylic acid compounds for the present invention.

Canadian Patent 1 183 125; US Patent Publication numbers 2006/0183647and US-2006-0079413; U.S. Patent Application No. 60/867,402; and BritishPatent 2 105 743 A, all disclose useful examples of suitable tartaricacid derivatives.

The compound derived from the hydroxy-carboxylic acid may be present at0.01 wt % to 3 wt %, or 0.01 wt % to 1 wt %, or 0.05 wt % to 0.5 wt %,or 0.1 wt % to 0.2 wt % of the lubricating composition.

Phosphorus Compound

The phosphorus compound may be selected from the group consisting of anamine salt of a phosphate hydrocarbon ester, a phosphite having at leastone hydrocarbyl group with 4 or more carbon atoms, having at least onehydrocarbyl group with 4 or more carbon atoms, and mixtures thereof.

In one embodiment the phosphorus compound is sulphur-free i.e., thephosphorus compound is not a thiophosphite, nor a thiophosphate.

The phosphorus compound may be present at 0.01 wt % to 5 wt %, or 0.05wt % to 2 wt %, or 0.1 wt % to 1 wt %, or 0.2 wt % to 0.4 wt % of thelubricating composition. The amount of phosphorus provided to thelubricating composition by the phosphorus compound may, in certainembodiments, be 0.001 to 0.5 wt %, or 0.005 to 0.2 wt %, or 0.01 to 0.1wt % or 0.02 to 0.04 wt %.

Amine Salt of a Phosphate Hydrocarbon Ester

In one embodiment the lubricating composition contains a phosphoruscompound that may be an amine salt of a phosphate hydrocarbon ester(i.e., an amine salt of a hydrocarbon ester of phosphoric acid). Theamine salt of a phosphate hydrocarbon ester may be derived from an aminesalt of a phosphate. The amine salt of the phosphate hydrocarbon estermay be represented by the formula:

whereinR³ and R⁴ may be independently hydrogen or hydrocarbon typicallycontaining 4 to 40, or 6 to 30, or 6 to 18, or 8 to 18 carbon atoms,with the proviso that at least one is a hydrocarbon group; andR⁵, R⁶, R⁷ and R⁸ may be independently hydrogen or a hydrocarbyl group,with the proviso that at least one is a hydrocarbyl group.

The hydrocarbon groups of R³ and/or R⁴ may be linear, branched, orcyclic.

Examples of a hydrocarbon group for R³ and/or R⁴ include straight-chainor branched alkyl groups include methyl, ethyl, propyl, butyl, pentyl,hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl,tetradecyl, pentadecyl, hexadecyl, heptadecyl and octadecyl.

Examples of a cyclic hydrocarbon group for R³ and/or R⁴ includecyclopentyl, cyclohexyl, cycloheptyl, methylcyclopentyl,dimethylcyclopentyl, methylcyclopentyl, dimethylcyclopentyl,methylethylcyclopentyl, diethyl-cyclopentyl, methylcyclohexyl,dimethylcyclohexyl, methylethylcyclohexyl, diethylcyclohexyl,methylcycloheptyl, dimethylcycloheptyl, methylethyl-cycloheptyl, anddiethylcycloheptyl.

In one embodiment the phosphate may be an amine salt of a mixture ofmonoalkyl and dialkyl phosphoric acid esters. The monoalkyl and dialkylgroups may be linear or branched.

The amine salt of a phosphate hydrocarbon ester may be derived from anamine such as a primary amine, a secondary amine, a tertiary amine, ormixtures thereof. The amine may be aliphatic, or cyclic, aromatic ornon-aromatic, typically aliphatic. In one embodiment the amine includesan aliphatic amine such as a tertiary-aliphatic primary amine.

Examples of suitable primary amines include ethylamine, propylamine,butylamine, 2-ethylhexylamine, bis-(2-ethylhexyl)amine, octyl-amine, anddodecylamine, as well as such fatty amines as n-octylamine,n-decylamine, n-dodecylamine, n-tetradecylamine, n-hexadecylamine,n-octa-decylamine and oleyamine. Other useful fatty amines includecommercially available fatty amines such as “Armeen®” amines (productsavailable from Akzo Chemicals, Chicago, Ill.), such as Armeen C, ArmeenO, Armeen O L, Armeen T, Armeen H T, Armeen S and Armeen S D, whereinthe letter designation relates to the fatty group, such as coco, oleyl,tallow, or stearyl groups.

Examples of suitable secondary amines include dimethylamine,diethylamine, dipropylamine, dibutylamine, diamylamine, dihexylamine,diheptylamine, methylethylamine, ethylbutylamine,N-methyl-1-amino-cyclohexane, Armeen® 2C and ethylamylamine. Thesecondary amines may be cyclic amines such as piperidine, piperazine andmorpholine.

Examples of tertiary amines include tri-n-butylamine, tri-n-octylamine,tri-decylamine, tri-laurylamine, tri-hexadecylamine, anddimethyloleylamine (Armeen® DMOD).

In one embodiment the amines are in the form of a mixture. Examples ofsuitable mixtures of amines include (i) a tertiary alkyl primary aminewith 11 to 14 carbon atoms, (ii) a tertiary alkyl primary amine with 14to 18 carbon atoms, or (iii) a tertiary alkyl primary amine with 18 to22 carbon atoms. Other examples of tertiary alkyl primary amines includetert-butylamine, tert-hexylamine, tert-octylamine (such as1,1-dimethylhexylamine), tert-decylamine (such as1,1-dimethyloctylamine), tertdodecylamine, tert-tetradecylamine,tert-hexadecylamine, tert-octadecylamine, tert-tetracosanylamine, andtert-octacosanylamine.

In one embodiment a useful mixture of amines is “Primene® 81 R” or“Primene® JMT.” Primene® 81R and Primene® JMT (both produced and sold byRohm & Haas) are mixtures of C11 to C14 tertiary alkyl primary aminesand C18 to C22 tertiary alkyl primary amines respectively.

The amine salt of a phosphate hydrocarbon ester may be prepared as isdescribed in U.S. Pat. No. 6,468,946. Column 10, lines 15 to 63describes phosphoric acid esters formed by reaction of phosphoruscompounds, followed by reaction with an amine to form an amine salt of aphosphate hydrocarbon ester. Column 10, line 64, to column 12, line 23,describes preparative examples of reactions between phosphorus pentoxidewith an alcohol (having 4 to 13 carbon atoms), followed by a reactionwith an amine (typically Primene®81-R) to form an amine salt of aphosphate hydrocarbon ester.

Phosphite

In one embodiment the lubricating composition contains a phosphitehaving at least one hydrocarbyl group with 4 or more carbon atoms. Inone embodiment the lubricating composition contains a phosphite havingat least one hydrocarbyl group with 8 or more, or 12 or more carbonatoms. Typical ranges for the number of carbon atoms on the hydrocarbylgroup include 4 to 30, or to 24, or 12 to 22, or 14 to 20, or 16 to 18.The phosphite may be a mono-hydrocarbyl substituted phosphite, adi-hydrocarbyl substituted phosphite, or a tri-hydrocarbyl substitutedphosphite.

The phosphite having at least one hydrocarbyl group with 4 or morecarbon atoms may be represented by the formulae:

wherein at least one or two of R⁹, R¹⁰ and R¹¹ may be a hydrocarbylgroup containing at least 4 carbon atoms and the other may be hydrogenor a hydrocarbyl group. In one embodiment two or more of R⁹, R¹⁰ and R¹¹are hydrocarbyl groups. The hydrocarbyl groups may be alkyl, cycloalkyl,aryl, acyclic or mixtures thereof. In the formula with all three groupsR⁹, R¹⁰ and R¹¹, the compound may be a tri-hydrocarbyl substitutedphosphite i.e., R⁹, R¹⁰ and R¹¹ are all hydrocarbyl groups.

Alkyl groups may be linear or branched, typically linear, and saturatedor unsaturated, typically saturated. Examples of alkyl groups for R⁹,R¹⁰ and R¹¹ include butyl, hexyl, octyl, 2-ethylhexyl, nonyl, decyl,undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl,heptadecyl, octadecyl, octadecenyl, nonodecyl, eicosyl or mixturesthereof.

Alkyl groups may be linear or branched, typically linear, and saturatedor unsaturated, typically saturated. Examples of alkyl groups for R⁹,R¹⁰ and R¹¹ include butyl, hexyl, octyl, 2-ethylhexyl, nonyl, decyl,undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl,heptadecyl, octadecyl, octadecenyl, nonodecyl, eicosyl or mixturesthereof. In one embodiment the alkyl groups R⁹ and R¹⁰ have 4 carbonatoms (typically n-butyl).

The amine salt of a phosphate hydrocarbon ester and/or, a phosphitehaving at least one hydrocarbyl group with 4 or more carbon atoms may inone embodiment be in a mixture with one or more of phosphorus acid,phosphoric acid, polyphosphoric acid, a trialkyl phosphate or trialkylthiophosphate. For instance the amine salt of a phosphate hydrocarbonester and/or, a phosphite having at least one hydrocarbyl group with 4or more carbon atoms may in one embodiment be in a mixture withphosphoric acid.

Oils of Lubricating Viscosity

The lubricating composition comprises an oil of lubricating viscosity.Such oils include natural and synthetic oils, oil derived fromhydrocracking, hydrogenation, and hydrofinishing, unrefined, refined,re-refined oils or mixtures thereof. A more detailed description ofunrefined, refined and re-refined oils is provided in InternationalPublication WO2008/147704, paragraphs [0054] to

A more detailed description of natural and synthetic lubricating oils isdescribed in paragraphs [0058] to [0059] respectively of WO2008/147704.Synthetic oils may also be produced by Fischer-Tropsch reactions andtypically may be hydroisomerised Fischer-Tropsch hydrocarbons or waxes.In one embodiment oils may be prepared by a Fischer-Tropschgas-to-liquid synthetic procedure as well as other gas-to-liquid oils.

Oils of lubricating viscosity may also be defined as specified in April2008 version of “Appendix E—API Base Oil Interchangeability Guidelinesfor Passenger Car Motor Oils and Diesel Engine Oils”, section 1.3Sub-heading 1.3. “Base Stock Catagories”. In one embodiment the oil oflubricating viscosity may be an API Group I, or Group II, or Group III,or Group IV oil. In one embodiment the oil of lubricating viscosity maybe an API Group II or Group III oil. In one embodiment the oil oflubricating viscosity may be a hydrocracked or severely hydrocrackedbase stock and/or an API Group II or Group III oil.

The amount of the oil of lubricating viscosity present is typically thebalance remaining after subtracting from 100 wt % the sum of the amountof the compound of the invention and the other performance additives.

The lubricating composition may be in the form of a concentrate and/or afully formulated lubricant. If the lubricating composition of theinvention (comprising the additives disclosed herein) is in the form ofa concentrate which may be combined with additional oil to form, inwhole or in part, a finished lubricant), the ratio of the of theseadditives to the oil of lubricating viscosity and/or to diluent oilinclude the ranges of 1:99 to 99:1 by weight, or 80:20 to 10:90 byweight.

Organo-Sulphide

In one embodiment the lubricating composition further comprises anorgano-sulphide, or mixtures thereof. In one embodiment theorgano-sulphide comprises at least one of a polysulphide, thiadiazolecompound, or mixtures thereof.

In different embodiments, the organo-sulphide is present in a rangeselected from the group consisting of 0 wt % to 10 wt %, 0.01 wt % to 10wt %, 0.1 wt % to 8 wt %, and 0.25 wt % to 6 wt %; of the lubricatingcomposition.

Thiadiazole Compound

Examples of a thiadiazole include 2,5-dimercapto-1,3,4-thiadiazole, oroligomers thereof, a hydrocarbyl-substituted2,5-dimercapto-1,3,4-thiadiazole, a hydrocarbylthio-substituted2,5-dimercapto-1,3,4-thiadiazole, or oligomers thereof. The oligomers ofhydrocarbyl-substituted 2,5-dimercapto-1,3,4-thiadiazole typically formby forming a sulphur-sulphur bond between2,5-dimercapto-1,3,4-thiadiazole units to form oligomers of two or moreof said thiadiazole units. These thiadiazole compounds may also be usedin the post treatment of dispersants as mentioned below in the formationof a dimercaptothiadiazole derivative of a polyisobutylene succinimide.

Examples of a suitable thiadiazole compound include at least one of adimercaptothiadiazole, 2,5-dimercapto-[1,3,4]-thiadiazole,3,5-dimercapto-[1,2,4]-thiadiazole, 3,4-dimercapto-[1,2,5]-thiadiazole,or 4-5-dimercapto-[1,2,3]-thiadiazole. Typically readily availablematerials such as 2,5-dimercapto-1,3,4-thiadiazole or ahydrocarbyl-substituted 2,5-dimercapto-1,3,4-thiadiazole or ahydrocarbylthio-substituted 2,5-dimercapto-1,3,4-thiadiazole arecommonly utilised. In different embodiments the number of carbon atomson the hydrocarbyl-substituent group includes 1 to 30, 2 to 25, 4 to 20,6 to 16, or 8 to 10.

In one embodiment, the thiadiazole compound is the reaction product of aphenol with an aldehyde and a dimercaptothiadiazole. The phenol includesan alkyl phenol wherein the alkyl group contains at least 6, e.g., 6 to24, or 6 (or 7) to 12 carbon atoms. The aldehyde includes an aldehydecontaining 1 to 7 carbon atoms or an aldehyde synthon, such asformaldehyde. Useful thiadiazole compounds include2-alkyldithio-5-mercapto-[1,3,4]-thiadiazoles,2,5-bis(alkyl-dithio)-[1,3,4]-thiadiazoles,2-alkylhydroxyphenylmethylthio-5-mercapto-[1,3,4]-thiadiazoles (such as2-[5-heptyl-2-hydroxyphenylmethylthio]-5-mercapto-[1,3,4]-thiadiazole),and mixtures thereof.

In one embodiment the thiadiazole compound includes at least one of2,5-bis(tert-octyldithio)-1,3,4-thiadiazole,2,5-bis(tert-nonyldithio)-1,3,4-thiadiazole, or2,5-bis(tert-decyldithio)-1,3,4-thiadiazole.

Polysulphide

In one embodiment at least 50 wt % of the polysulphide molecules are amixture of tri- or tetra-sulphides. In other embodiments at least 55 wt%, or at least 60 wt % of the polysulphide molecules are a mixture oftri- or tetra-sulphides.

The polysulphide includes a sulphurised organic polysulphide from oils,fatty acids or ester, olefins or polyolefins.

Oils which may be sulfurized include natural or synthetic oils such asmineral oils, lard oil, carboxylate esters derived from aliphaticalcohols and fatty acids or aliphatic carboxylic acids (e.g., myristyloleate and oleyl oleate), and synthetic unsaturated esters orglycerides.

Fatty acids include those that contain 8 to 30, or 12 to 24 carbonatoms. Examples of fatty acids include oleic, linoleic, linolenic, andtall oil. Sulphurised fatty acid esters prepared from mixed unsaturatedfatty acid esters such as are obtained from animal fats and vegetableoils, including tall oil, linseed oil, soybean oil, rapeseed oil, andfish oil.

The polysulphide includes olefins derived from a wide range of alkenes.The alkenes typically have one or more double bonds. The olefins in oneembodiment contain 3 to 30 carbon atoms. In other embodiments, olefinscontain 3 to 16, or 3 to 9 carbon atoms. In one embodiment thesulphurised olefin includes an olefin derived from propylene,isobutylene, pentene or mixtures thereof.

In one embodiment the polysulphide comprises a polyolefin derived frompolymerising by known techniques, an olefin as described above.

In one embodiment the polysulphide includes dibutyl tetrasulphide,sulphurised methyl ester of oleic acid, sulphurised alkylphenol,sulphurised dipentene, sulphurised dicyclopentadiene, sulphurisedterpene, and sulphurised Diels-Alder adducts.

Friction Modifier

In one embodiment the lubricating composition further comprises afriction modifier. In different embodiments, the friction modifier ispresent in a range selected from the group consisting of 0 wt % to 5 wt%, 0.1 wt % to 4 wt %, 0.25 wt % to 3.5 wt %, 0.5 wt % to 2.5 wt %, and1 wt % to 2.5 wt %, or 0.05 wt % to 0.5 wt % of the lubricatingcomposition.

The friction modifier includes fatty amines, borated glycerol esters,fatty acid amides, non-borated fatty epoxides, borated fatty epoxides,alkoxylated fatty amines, borated alkoxylated fatty amines, metal saltsof fatty acids, fatty imidazolines, metal salts of alkyl salicylates(may also be referred to as a detergent), metal salts of sulphonates(may also be referred to as a detergent), condensation products ofcarboxylic acids or polyalkylene-polyamines, or amides of hydroxyalkylcompounds.

In one embodiment the friction modifier includes a fatty acid ester ofglycerol. The final product may be in the form of a metal salt, anamide, an imidazoline, or mixtures thereof. The fatty acids may contain6 to 24, or 8 to 18 carbon atoms. The fatty acids may branched orstraight-chain, saturated or unsaturated. Suitable acids include2-ethylhexanoic, decanoic, oleic, stearic, isostearic, palmitic,myristic, palmitoleic, linoleic, lauric, and linolenic acids, and theacids from the natural products tallow, palm oil, olive oil, peanut oil,corn oil, and Neat's foot oil. In one embodiment the fatty acid is oleicacid. When in the form of a metal salt, typically the metal includeszinc or calcium; and the products include overbased and non-overbasedproducts. Examples are overbased calcium salts and basic oleic acid-zincsalt complexes which can be represented by the general formulaZn₄Oleate₆O. When in the form of an amide, the condensation productincludes those prepared with ammonia, or with primary or secondaryamines such as diethylamine and diethanolamine. When in the form of animidazoline, the condensation product of an acid with a diamine orpolyamine such as a polyethylenepolyamine. In one embodiment thefriction modifier is the condensation product of a fatty acid with C8 toC24 atoms, and a polyalkylene polyamine, and in particular, the productof isostearic acid with tetraethylenepentamine.

In one embodiment the friction modifier includes those formed by thecondensation of the hydroxyalkyl compound with an acylating agent or anamine. A more detailed description of the hydroxyalkyl compound isdescribed in WO 2007/0044820 paragraphs 9, and 20-22. The frictionmodifier disclosed in WO2007/044820 includes an amide represented by theformula R¹²R¹³N—C(O)R¹⁴, wherein R¹² and R¹³ are each independentlyhydrocarbyl groups of at least 6 carbon atoms and R¹⁴ is a hydroxyalkylgroup of 1 to 6 carbon atoms or a group formed by the condensation ofsaid hydroxyalkyl group, through a hydroxyl group thereof, with anacylating agent. Preparative Examples are disclosed in Examples 1 and 2(paragraphs 72 and 73 of WO2007/044820). In one embodiment the amide ofa hydroxylalkyl compound is prepared by reacting glycolic acid, that is,hydroxyacetic acid, HO—CH₂—COOH with an amine.

In one embodiment the friction modifier includes a secondary or tertiaryamine being represented by the formula R¹⁵R¹⁶NR¹⁷ ₅ wherein R¹⁵ and R¹⁶are each independently an alkyl group of at least 6 carbon atoms and R¹⁷is hydrogen, a hydrocarbyl group, a hydroxyl-containing alkyl group, oran amine-containing alkyl group. A more detailed description of thefriction modifier is described in US Patent Application 2005/037897 inparagraphs 8 and 19 to 22.

In one embodiment the friction modifier includes a reaction product of adi-cocoalkyl amine (or di-cocoamine) with glycolic acid. The frictionmodifier includes compounds prepared in Preparative Examples 1 and 2 ofWO 2008/014319.

In one embodiment the friction modifier includes those derived from thereaction product of a carboxylic acid or a reactive equivalent thereofwith an aminoalcohol, wherein the friction modifier contains at leasttwo hydrocarbyl groups, each containing at least 6 carbon atoms. Anexample of such a friction modifier includes the reaction product ofisostearic acid or an alkyl succinic anhydride withtris-hydroxymethylaminomethane. A more detailed description of such afriction modifier is disclosed in US Patent Application 2003/22000 (orInternational Publication WO04/007652) in paragraphs 8 and 9 to 14.

In one embodiment the friction modifier includes an alkoxylated alcohol.A detailed description of suitable alkoxylated alcohols is described inparagraphs 19 and 20 of US Patent Application 2005/0101497. Thealkoxylated amines are also described in U.S. Pat. No. 5,641,732 incolumn 7, line 15 to column 9, line 25.

In one embodiment the friction modifier includes a hydroxylaminecompound as defined in column 37, line 19, to column 39, line 38 of U.S.Pat. No. 5,534,170. Optionally the hydroxylamine includes borated assuch products are described in column 39, line 39 to column 40 line 8 ofU.S. Pat. No. 5,534,170.

In one embodiment the friction modifier includes an alkoxylated aminee.g., an ethoxylated amine derived from 1.8% Ethomeen™ T-12 and 0.90%Tomah™ PA-1 as described in Example E of U.S. Pat. No. 5,703,023, column28, lines 30 to 46. Other suitable alkoxylated amine compounds includecommercial alkoxylated fatty amines known by the trademark “ETHOMEEN”and available from Akzo Nobel. Representative examples of theseETHOMEEN™ materials is ETHOMEEN™ C/12 (bis[2-hydroxyethyl]-coco-amine);ETHOMEEN™ C/20 (polyoxyethylene[10]cocoamine); ETHOMEEN™ S/12(bis[2-hydroxyethyl]soyamine); ETHOMEEN™ T/12(bis[2-hydroxyethyl]allow-amine); ETHOMEEN™ T/15(polyoxyethylene-[5]tallowamine); ETHOMEEN™ 0/12(bis[2-hydroxyethyl]oleyl-amine); ETHOMEEN™ 18/12(bis[2-hydroxyethyl]octadecylamine); and ETHOMEEN™ 18/25(polyoxyethylene[15]octadecylamine). Fatty amines and ethoxylated fattyamines are also described in U.S. Pat. No. 4,741,848.

In one embodiment the friction modifier includes a polyol ester asdescribed in U.S. Pat. No. 5,750,476 column 8, line 40 to column 9, line28.

In one embodiment the friction modifier includes a low potency frictionmodifier as described in U.S. Pat. No. 5,840,662 in column 2, line 28 tocolumn 3, line 26. U.S. Pat. No. 5,840,662 further discloses in column3, line 48 to column 6, line 25 specific materials and methods ofpreparing the low potency friction modifier.

In one embodiment the friction modifier includes a reaction product ofan isomerised alkenyl substituted succinic anhydride and a polyamine asdescribed in U.S. Pat. No. 5,840,663 in column 2, lines 18 to 43.Specific embodiments of the friction modifier described in U.S. Pat. No.5,840,663 are further disclosed in column 3, line 23 to column 4, line35. Preparative examples are further disclosed in column 4, line 45 tocolumn 5, line 37 of U.S. Pat. No. 5,840,663.

In one embodiment the friction modifier includes an alkylphosphonatemono- or di-ester sold commercially by Rhodia under the trademarkDuraphos® DMODP.

In one embodiment the friction modifier includes a borated fatty epoxideor alkylene oxide, known from Canadian Patent No. 1,188,704. Theseoil-soluble boron-containing compositions are prepared by reacting, at atemperature of 80° C. to 250° C., boric acid or boron trioxide with atleast one fatty epoxide or alkylene oxide. The fatty epoxide or alkyleneoxide typically contains at least 8 carbon atoms in the fatty groups ofthe epoxide (or the alkylene groups of the alkylene oxide).

The borated fatty epoxides include those characterised by the method fortheir preparation which involves the reaction of two materials. ReagentA includes boron trioxide or any of the various forms of boric acidincluding metaboric acid (HBO₂), orthoboric acid (H₃BO₃) and tetraboricacid (H₂B₄O₇), or orthoboric acid. Reagent B includes at least one fattyepoxide. The molar ratio of reagent A to reagent B is generally 1:0.25to 1:4, or 1:1 to 1:3, or 1:1 to 1:2. The borated fatty epoxidesincludes compounds prepared by blending the two reagents and heatingthem at temperature of 80° C. to 250° C., or 100° C. to 200° C., for aperiod of time sufficient for reaction to take place. If desired, thereaction may be effected in the presence of a substantially inert,normally liquid organic diluent. During the reaction, water is evolvedand may be removed by distillation.

Other Performance Additive

The composition of the invention optionally further includes at leastone other performance additive. The other performance additives includemetal deactivators, detergents, dispersants, viscosity modifiers,dispersant viscosity modifiers, antioxidants, corrosion inhibitors, foaminhibitors, demulsifiers, pour point depressants, seal swelling agents,and mixtures thereof.

In different embodiments, the total combined amount of the otherperformance additive compounds is present in a range selected from thegroup consisting of 0 wt % to 25 wt %, 0.1 wt % to 15 wt %, and 0.5 wt %to 10 wt %, of the lubricating composition. Although one or more of theother performance additives may be present, it is common for the otherperformance additives to be present in different amounts relative toeach other.

Antioxidants include molybdenum compounds such as molybdenumdithiocarbamates, sulphurised olefins, hindered phenols, aminiccompounds such as alkylated diphenylamines (typically di-nonyldiphenylamine, octyl diphenylamine, or di-octyl diphenylamine).

Detergents include neutral or overbased detergents, Newtonian ornon-Newtonian, basic salts of alkali, alkaline earth or transitionmetals with one or more of a phenate, a sulphurised phenate, asulphonate, a carboxylic acid, a phosphorus acid, a mono- and/or adi-thiophosphoric acid, a saligenin, an alkylsalicylate, and asalixarate.

Dispersants are known and include for example an N-substituted longchain alkenyl succinimide, a Mannich base, or mixtures thereof. Examplesof N-substituted long chain alkenyl succinimides include polyisobutylenesuccinimide, wherein the polyisobutylene from which the polyisobutylenesuccinic anhydride is derived has a number average molecular weight inthe range of 350 to 5000, or 500 to 3000, or 750 to 1150.

The dispersants may also be post-treated by conventional methods by areaction with any of a variety of agents. Among these are boroncompounds (such as boric acid), urea, thiourea, dimercaptothiadiazoles,carbon disulphide, aldehydes, ketones, carboxylic acids such asterephthalic acid, hydrocarbon-substituted succinic anhydrides, maleicanhydride, nitriles, epoxides, and phosphorus compounds. In oneembodiment the post-treated dispersant may be a borated dispersant suchas a borated polyisobutylene succinimide. In one embodiment thepost-treated dispersant may be made by reaction with adimercaptothiadiazole (to form a dispersant such as adimercaptothiadiazole derivative of a polyisobutylene succinimide).

In different embodiments, the dispersant is present in a range selectedfrom the group consisting of 0 wt % to 10 wt %, 0.01 wt % to 10 wt %,and 0.1 wt % to 5 wt %, of the lubricating composition.

Viscosity modifiers include hydrogenated copolymers ofstyrene-butadiene, ethylene-propylene copolymers, polyisobutenes,hydrogenated styrene-isoprene polymers, hydrogenated isoprene polymers,polymethacrylate acid esters, polyacrylate acid esters, polyalkylstyrenes, alkenyl aryl conjugated diene copolymers, polyolefins,polyalkylmethacrylates and esters of maleic anhydride-styrenecopolymers. Dispersant viscosity modifiers (often referred to as DVM)include functionalised polyolefins, for example, ethylene-propylenecopolymers that have been functionalized with the reaction product ofmaleic anhydride and an amine, a polymethacrylate functionalised with anamine, or styrene-maleic anhydride copolymers reacted with an amine; mayalso be used in the composition of the invention.

Corrosion inhibitors include octylamine octanoate, condensation productsof dodecenyl succinic acid or anhydride and a fatty acid such as oleicacid with a polyamine, or a thiadiazole compound described above. Metaldeactivators include derivatives of benzotriazoles (typicallytolyltriazole), 1,2,4-triazoles, benzimidazoles,2-alkyldithiobenzimidazoles or 2-alkyldithiobenzothiazoles.

Foam inhibitors include for example copolymers of ethyl acrylate and2-ethylhexylacrylate and optionally vinyl acetate. Demulsifiers includetrialkyl phosphates, polyethylene glycols, polyethylene oxides,polypropylene oxides and (ethylene oxide-propylene oxide) polymers. Pourpoint depressants include esters of maleic anhydride-styrene,polymethacrylates, polyacrylates or polyacrylamides. Seal swell agentsinclude Exxon Necton-37™ (FN 1380) and Exxon Mineral Seal Oil (FN 3200).

INDUSTRIAL APPLICATION

The method of the invention is useful for lubricating a variety ofdriveline devices applications. The driveline device comprises at leastone of a gear, a gearbox, an axle gear, a traction drive transmission,an automatic transmission or a manual transmission. In one embodimentthe driveline device is a manual transmission or a gear, a gearbox, oran axle gear.

The automatic transmission includes continuously variable transmissions(CVT), infinitely variable transmissions (IVT), Torroidal transmissions,continuously slipping torque converted clutches (CSTCC), steppedautomatic transmissions or dual clutch transmissions (DCT).

In one embodiment the invention provides for the use of the lubricatingcomposition disclosed herein in gears and transmissions to impart atleast one of antiwear performance, extreme pressure performance,acceptable deposit control, acceptable oxidation stability and reducedodour.

Unless otherwise indicated, each chemical or composition referred toherein should be interpreted as being a commercial grade material whichmay contain the isomers, by-products, derivatives, and other suchmaterials which are normally understood to be present in the commercialgrade. However, the amount of each chemical component is presentedexclusive of any solvent or diluent oil, which may be customarilypresent in the commercial material, unless otherwise indicated.

The following examples provide illustrations of the invention. Theseexamples are non-exhaustive and are not intended to limit the scope ofthe invention.

EXAMPLES

Lubricant Example 1 (EX1) is a 80W-90 gear oil lubricant containing 0.4wt % of a Primene®81-R amine salt of oleyl phosphate and 0.15 wt % of2-ethylhexyl tartrate.

Comparative Lubricant Example 1 (CLE1) is a gear oil lubricant similarto EX1, except it does not contain the tartrate.

Lubricant Example 2 (EX2) is a 80W-90 gear oil lubricant containing 0.4wt % of a dibutyl phosphite and 0.15 wt % of 2-ethylhexyl tartrate.

Comparative Lubricant Example 2 (CLE2) is a gear oil lubricant similarto EX2, except it does not contain the tartrate.

Comparative Lubricant Example 3 (CLE3) is a gear oil lubricant similarto EX1, except it contains 0.15 wt % of 2-ethyl hexyl tartrate and 0.18wt % of an amine salt of a thiophosphate as described by preparativeexamples 6 to 8 of International Patent application WO US09/036623 asdescribed in paragraph [0107] of said application.

Comparative Lubricant Example 4 (CLE4) is a gear oil lubricant similarto EX1, except contains 0.18 wt % of an amine salt of a phosphate asdescribed by preparative examples 1 to 4 of International Patentapplication WO US09/036623 as described in paragraphs [0099] to [0105]of said application.

Lubricant Example 3 (EX3) is an 80W-90 gear oil lubricant containing 1wt % of a Primene®81-R amine salt of oleyl phosphate, 0.25 wt % ofdibutyl phosphite, and 0.1 wt % of 2-ethylhexyl tartrate.

Lubricant Example 4 (EX4) is a 75W-90 gear oil lubricant containing 0.8wt % of a Primene®81-R amine salt of oleyl phosphate, 0.5 wt % ofdibutyl phosphite, and 0.2 wt % of 2-ethylhexyl tartrate.

Lubricants CLE1 to CLE4 and EX1 to EX4 are evaluated by themethodologies of ASTM D6121-05a (the L-37 Gear Durability Test), andL-42 Axle Shock Test method described in ASTM publication STP 512A.Typically better results in the L-42 test are for samples with lowerpercent rating of ring and pinion scoring. Typically, better results inthe L-37 test are obtained for samples with higher numbers.

The results obtained for EX1 and comparative examples CLE1, CLE3 andCLE4 at the end of the L-42 test are as follows:

Ring Ring Pinion Pinion Drive Coast Drive Coast EX1 0 13 0 17 CLE1 0 210 29 CLE3 0 57 0 34 CLE4 0 92 0 66

The results of the L-42 test indicate that the composition of theinvention has reduced ring and pinion scoring compared to similarcompositions containing other antiwear additives. For example thelubricating composition disclosed herein has improved performance in theL-42 test over compositions similar to those disclosed in InternationalPatent application WO US09/036623 (i.e., CLE3 and CLE4).

The results obtained for EX1 and comparative example CLE1 at the end ofthe L-37 test are as follows:

Parameter Rated on Ring EX1 CLE1 Ring Wear Final Wear Rating 8 7 FinalSurface Fatigue Rippling 10 9 Final Surface Fatigue Ridging 10 7 FinalSurface Fatigue Pitting and 9.9 9.9 Spalling Merit Final Surface FatigueScoring 10 10 Pinion Wear Final Wear Rating 8 6 Final Wear Rippling 9 8Final Wear Ridging 10 7 Final Wear Scoring 9.9 9.6 Final Pitting andSpalling Merit 10 10

The results of the L-37 test indicate that the composition of theinvention has reduced wear, rippling, ridging and scoring compared tosimilar compositions containing other antiwear phosphorus additives.

Overall, the compositions of the invention have performance benefitsover comparative examples in least one of (i) sulphur (typicallyreducing or preventing emissions from waste oil), (ii) fueleconomy/efficiency (typically improving fuel economy/efficiency), (iii)oxidation control (typically reducing or preventing oxidation), (iv)friction performance, (v) wear and/or extreme pressure performance(typically reducing or preventing), and (vi) deposit control.

It is known that some of the materials described above may interact inthe final formulation, so that the components of the final formulationmay be different from those that are initially added. The productsformed thereby, including the products formed upon employing lubricantcomposition of the present invention in its intended use, may not besusceptible of easy description. Nevertheless, all such modificationsand reaction products are included within the scope of the presentinvention; the present invention encompasses lubricant compositionprepared by admixing the components described above.

Each of the documents referred to above is incorporated herein byreference. Except in the Examples, or where otherwise explicitlyindicated, all numerical quantities in this description specifyingamounts of materials, reaction conditions, molecular weights, number ofcarbon atoms, and the like, are to be understood as modified by the word“about.” It is to be understood that the upper and lower amount, range,and ratio limits set forth herein may be independently combined.Similarly, the ranges and amounts for each element of the invention maybe used together with ranges or amounts for any of the other elements

As used herein, the term “hydrocarbyl substituent” or “hydrocarbylgroup” is used in its ordinary sense, which is well-known to thoseskilled in the art. Specifically, it refers to a group having a carbonatom directly attached to the remainder of the molecule and havingpredominantly hydrocarbon character. Examples of hydrocarbyl groupsinclude: hydrocarbon substituents, including aliphatic, alicyclic, andaromatic substituents; substituted hydrocarbon substituents, that is,substituents containing non-hydrocarbon groups which, in the context ofthis invention, do not alter the predominantly hydrocarbon nature of thesubstituent; and hetero substituents, that is, substituents whichsimilarly have a predominantly hydrocarbon character but contain otherthan carbon in a ring or chain. A more detailed definition of the term“hydrocarbyl substituent” or “hydrocarbyl group” is described inparagraphs [0118] to [0119] of International Publication WO2008147704.

As used herein the term “fatty” as in fatty acid (and other expressionsused herein) includes a hydrocarbyl chain containing 4 to 150, or 4 to30, or 6 to 16 carbon atoms.

While the invention has been explained in relation to its preferredembodiments, it is to be understood that various modifications thereofwill become apparent to those skilled in the art upon reading thespecification. Therefore, it is to be understood that the inventiondisclosed herein is intended to cover such modifications as fall withinthe scope of the appended claims.

What is claimed is:
 1. A method for lubricating a driveline devicecomprising supplying to the driveline device a lubricating compositioncomprising an oil of lubricating viscosity and an antiwear packagewherein the antiwear package comprises (a) 0.01 wt % to 3 wt % of aderivative of a hydroxycarboxylic acid, wherein the derivative of ahydroxycarboxylic acid is represented by the formula:

wherein n=2, m=1, or n and m both equal 2, or n=3, m=1; X is analiphatic or alicyclic group, or an aliphatic or alicyclic groupcontaining an oxygen atom in the carbon chain, or a substituted group ofthe foregoing types, said group containing up to 6 carbon atoms andhaving n+m available points of attachment; each Y is independently —O—,or >NR¹ or two Ys together representing the nitrogen of an imidestructure R—N<formed between two carbonyl groups; and each R and R¹ areindependently hydrogen or a hydrocarbyl group, provided that at leastone R or R¹ group is a hydrocarbyl group; each R² is independentlyhydrogen, a hydrocarbyl group or an acyl group, further provided that atleast one —OR² group is located on a carbon atom within X that is α or βto at least one of the —C(O)—Y—R groups, and (b) 0.05 wt % to 2 wt % ofa phosphorus compound, wherein the phosphorus compound is an amine saltof a phosphate hydrocarbon ester represented by the formula:

wherein R³ and R⁴ are independently hydrogen or hydrocarbon containing 4to 40 carbon atoms, with the proviso that at least one is a hydrocarbongroup; and R⁵, R⁶, R⁷ and R⁸ independently hydrogen or a hydrocarbylgroup, with the proviso that at least one is a hydrocarbyl group.
 2. Themethod of claim 1, wherein the hydroxy-carboxylic acid is tartaric acidor citric acid.
 3. The method of claim 1, wherein the hydroxy-carboxylicacid is present at 0.01 wt % to 1 wt % of the lubricating composition.4. The method of claim 1, wherein the hydroxy-carboxylic acid is presentat 0.1 wt % to 0.2 wt % of the lubricating composition.
 5. The method ofclaim 1, wherein the phosphorus compound is sulphur-free.
 6. The methodof claim 1, wherein R³ and R⁴ are independently hydrogen or hydrocarboncontaining 8 to 18 carbon atoms, with the proviso that at least one is ahydrocarbon group.
 7. The method of claim 1, wherein the phosphoruscompound is a mixture of an amine salt of a phosphate hydrocarbon ester,and a phosphite having at least one hydrocarbyl group with 4 or morecarbon atoms.
 8. The method of claim 7, wherein the phosphite is amono-hydrocarbyl substituted phosphite, a di-hydrocarbyl substitutedphosphite, or a tri-hydrocarbyl substituted phosphite.
 9. The method ofclaim 7, wherein the phosphite having at least one hydrocarbyl groupwith 4 or more carbon atoms is represented by the formulae:

wherein at least two of R⁹, R¹⁰ and R¹¹ may be a hydrocarbyl groupcontaining at least 4 carbon atoms and the other may be hydrogen or ahydrocarbyl group.
 10. The method of claim 1, wherein the phosphoruscompound is present at 0.1 wt % to 1 wt % of the lubricatingcomposition.
 11. The method of claim 1, wherein the phosphorus compoundis present at 0.2 wt % to 0.4 wt % of the lubricating composition. 12.The method of claim 1 further comprising an organo-sulphide, wherein theorgano-sulphide comprises at least one of a polysulphide, a thiadiazolecompound, or mixtures thereof.
 13. The method of claim 1 furthercomprising a borated polyisobutylene succinimide, or adimercaptothiadiazole derivative of a polyisobutylene succinimide. 14.The method of claim 1, wherein (a) the derivative of a hydroxycarboxylicacid is present at 0.01 wt % to 1 wt % of the lubricating composition;and (b) wherein the phosphorus compound is present at 0.05 wt % to 2 wt% of the lubricating composition.
 15. The method of claim 1, wherein (a)the derivative of a hydroxycarboxylic acid is present at 0.05 wt % to0.5 wt % of the lubricating composition; and (b) wherein the phosphoruscompound is present at 0.1 wt % to 1 wt % of the lubricatingcomposition.